Omnidirectional Monolithic Marker for Intraoperative MR-based Positional Sensing in Closed MRI
The advances in wireless tracking markers (e.g., solenoid coil, planar coil, double helix inductor, and split-ring structures) have enabled precise targeting and control during surgical operations, such as biopsy procedure, neurosurgery, renal denervation, and brachytherapy, etc. However, the majority of their designs encountered the same problem of orientation dependency, such that the signal-noise-ratio drops to its minimum when the inductor surface normal aligns to the MRI static magnetic field. This is because the degree of magnetic flux coupling, and hence the level of signal increase has orientation dependency. To this end, we propose an inductively coupled radio frequency (ICRF) marker for magnetic resonance (MR)-based positional tracking, enabling the robust increase of tracking signal at all scanning orientations in quadrature-excited closed MR imaging (MRI). The marker employs three curved resonant circuits fully covering a cylindrical surface that encloses the signal source. Each resonant circuit is a planar spiral inductor with parallel plate capacitors fabricated monolithically on flexible printed circuit board (FPC) and bent to achieve the curved structure. Size of the constructed marker is Ø3 mm × 5 mm with quality factor > 22, and its tracking performance was validated with 1.5 T MRI scanner. As result, the marker remains as a high positive contrast spot under 360° rotations in 3 axes. The marker can be accurately localized with a maximum error of 0.56 mm under a displacement of 56 mm from the isocenter, along with an inherent standard deviation of 0.1 mm. This marker targets applications that can involve rotational changes in all axes (X-Y-Z).
[Video: Omnidirectional Monolithic Marker for Intra-operative MR-based Positional Sensing in Closed MRI
Fast MR Image Registration for MRI-guided Intervention
Magnetic Resonance Imaging (MRI) offers high resolution images to visualize soft tissue details, allowing clinicians to identify critical regions such as tumors margins and neurovascular and muscular structures. To visualize physiological changes of soft tissues during surgical intervention, fast image registration techniques are necessary to align pre-operative and intra-operative images. We are developing navigation systems that enable intra-operative MRI-guided interventions. The main components are i) fast image registration using advanced computing units (e.g. graphical computing units (GPUs), field-programmable gate arrays (FPGAs)), so as to achieve high-quality intra-operative MRI; ii) miniaturized MR tracking units for accurate and rapid positional sensing of surgical tools, which close the loop of the intervention; and iii) human-robot control interface that provide allows intuitive manipulation of robotic surgical tools. These components are particularly beneficial to minimal invasive surgeries (MIS) such as cardiac electrophysiology, deep brain stimulation, transoral surgery, etc., providing safe, precise and effective control of surgical instruments.
Wireless Multilayer Tracking Marker for MRI-guided Intervention
Magnetic Resonance (MR) compatible wireless markers can provide 3D positional tracking under MR imaging, which would facilitate MRI-guided navigation of interventional tools, in particular for those assisted by tele-operated robots. However, a major hurdle is the integration of wireless markers with surgical instruments, which requires small size but still sufficient quality factor. To this end, we propose a new design and fabrication approach of a tiny and thin wireless MR-tracking marker (6.7 mm × 1.5 mm × 0.3 mm), much smaller than those seen in prior art, but with a quality factor (Q factor 28.5) still comparable to them. This design and fabrication approach are reportedly the first design to initiate wireless markers in such a small size, enabling straightforward integration with interventional tools. When validated under MRI, the tracking marker appeared as a very high contrast spot on the MR images. For a 48 mm distance from the isocenter, the estimated maximum errors in 3D position was 0.48 mm. And the inherent standard deviation of marker localization was 0.12 mm. With the high MR contrast signal generated, the presented markers enable automatic and real-time tracking in 3D, but without MR image construction.
 C.L. Cheung, M. Wu, G. Fang, J.D.L. Ho, L. Liang, K. Tan, F.H. Lin, H.C. Chang, K.W. Kwok, “Omnidirectional Monolithic Marker for Intra-operative MR-based Positional Sensing in Closed MRI,” IEEE Transactions on Medical Imaging (TMI) (Accepted)
 C.L. Cheung, K.H. Lee, Z. Guo, Z. Dong, C.W. Leong, Y. Chen, P.W. Lee, K.W. Kwok, "Kinematic-model-free Positional Control for Robot-assisted Cardiac Catheterization", in the Proceedings of the Hamlyn Symposium on Medical Robotics, pp.80-81, 2016. Detail
 Y. Chen, W. Wang, E. J. Schmidt, K.W. Kwok, A. N. Viswanathan, R. Cormack, and Z. T. H. Tse, "Design and Fabrication of MR-Tracked Metallic Stylet for Gynecologic Brachytherapy," IEEE/ASME Transactions on Mechatronics, vol. 21, no. 2, pp.956-962, 2016. Detail
 K.W. Kwok, K.H. Lee, Y. Chen, W. Wang, Y. Hu, G.C.T. Chow, S.H. Zhang, W.G. Stevenson, R.Y. Kwong, W. Luk, E.J. Schmidt, Z.T.H. Tse, "Interfacing Fast Multi-phase Cardiac Image Registration with Real-time MRI-based Catheter Tracking for MRI-guided Electrophysiological Ablative Procedures," Circulation, 130(Suppl 2):A18568, 2014. Detail
1. Merit Poster Award in the IEEE International Conference on Robotics and Automation (ICRA) 2017, presented by the workshop C4 Surgical Robots: Compliant, Continuum, Cognitive, and Collaborative.
Authors and title: Z. Dong, Z. Guo, K.C.D. Fu, K.H. Lee, M.C.W. Leong, C.L. Cheung, A.P.W. Lee, W. Luk and K.W. Kwok, "A Robotic Catheter System for MRI-guided Cardiac Electrophysiological Intervention."
2. Best Live Demonstration prize – Surgical Robot Challenge 2016, organized by EPSRC UK-RAS Network.
Title: "MR-conditional Catheter Robot for MRI-guided Cardiac Electrophysiological Intervention."
1. PCT Provisional Pat: Robotic Catheter System for MRI-guided Cardiovascular Interventions: PCT/CN2017/089701 (Filed on 2017. Licensed by APTUS Therapeutics Limited.)
2. US Provisional Pat: Robotic Catheter System for MRI-guided Cardiovascular Interventions: US 15/630,406 (Filed on Jun 24, 2016. Licensed by APTUS Therapeutics Limited.)